jp5036629_si_002.xyz (6.21 kB)
Roles of Octabutoxy Substitution and J‑Aggregation in Stabilization of the Excited State in Nickel Phthalocyanine
dataset
posted on 2014-07-24, 00:00 authored by David Rais, Petr Toman, Jiří Černý, Miroslav Menšík, Jiří PflegerNickel
phthalocyanine (NiPc) complexes are known to show a rapid
nonradiative deactivation of the photoexcited state through the internal
conversion. This could be exploited in practical applications, such
as photoprotection and photodynamic therapy. The butoxy substitution
of NiPc plays an important role for drug delivery but also greatly
influences its photophysics. We prepared novel peripherally substituted
2,3,9,10,16,17,23,24-octabutoxy nickel(II) phthalocyanine and characterized
the deactivation pathway of its photoexcited state in solution by
femtosecond transient absorption spectroscopy and quantum chemical
calculations. We bring experimental evidence for the kinetic model,
in which the photoexcitation evolves in two independent branches.
In the first branch, assigned to the monomer, it undergoes ultrafast
intersystem crossing to a triplet state, which subsequently decays
to the ground state through a pathway involving lower-lying triplet
states, with a ground-state recovery lifetime of 814 ps. It is about
three-times longer than the lifetime published for unsubstituted NiPc.
In the second branch, the photoexcitation decayed to a triplet state
with an orders of magnitude longer lifetime, with the quantum yield
of about 4%. This state showed spectral features of J-aggregates.
These findings are important for the applications that rely on singlet
oxygen formation or fast nonradiative deactivation of the excited
state.